Apart from thyroid and blood sugar which your doctor mentioned, you may need following investigations too;
1) MRI of the brain with gadolinium contrast and sinuses (to rule out any lesion in brain and sinusitis).
2) Complete blood count and comprehensive metabolic panel (if not yet done).
The causes of dizziness and pressure in head according to the decreasing incidence are;
1) Benign paroxysmal positional vertigo (BPPV) 20%
2) Vestibular 15%
3) Migraine and motion sensitivity 15%
4) Anxiety and depression 10%
5) Meniere's disease 7%
6) Cerebellar disease 6%
7) Transient ischemic attacks 5%
8) Orthostatic hypotension 4%
Your physician may also consider MRA (magnetic resonance arteriography). That way any cause related to vascular disorder can be ruled out. MRI with gadolinium enhancement is particularly useful in detecting smaller intracanalicular tumors such as acoustic neuromas. It is also recommended for identifying sclerotic and demyelinating white matter lesions characteristic of multiple sclerosis. So that can be another investigation considered by your doctor. Chronic dizziness associated with the floating, rocking and light headedness and is induced by eye movements (head being still) should be also investigated or correlated to anxiety and depression, if all the medical imaging, blood work and examination is negative.
If you are on any medications, their side effects also should be ruled out for lightheadedness, as drugs are quite a common cause for this symptom. Dizziness may be provoked by only certain movements, such as standing up after lying down for at least 10 minutes in orthostatic hypotension, or may occur after vertical or oblique head movements, such as lying down, turning over in bed, or sitting up in benign paroxysmal positional vertigo (BPPV). Simply moving the eyes with the head stationary causes dizziness and there is no eye movement disorder (ocular misalignment or an internuclear ophthalmoparesis), then dizziness is likely to be the result of anxiety. When dizziness occurs without provocation (spontaneous) and is vestibular (ear disorder) in origin, it frequently is exacerbated by head movements.
Weakness in legs and nausea can be associated with some vascular lesion of brain or due to thyroid disorder.
Internal ear disease vertigo is termed true vertigo in which one feels rotational movement of self or the surroundings. The false vertigo or nonvertigo has feeling of light-headedness, unsteadiness, motion intolerance, imbalance, etc. You need to consult first an ENT specialist to exclude the diseases of internal ear. They will perform some clinical tests (vestibular diagnostic tests) to establish the cause. Often, dizziness can be a multisensory disorder due to any combination of peripheral neuropathy, visual impairment, and musculoskeletal disease. Many patients who have thyroid dysfunction can present with dizziness as an initial complaint. In individuals who have migraine, dizziness and vertigo can occur as part of the aura or separately. Spells usually last approximately an hour but can last several hours or days in patients who have severe symptoms. Most patients who have migraines have a long history of recurring symptoms. So that too should be assessed as a cause if you have a history of migraine.
That should be able to conclude for the diagnosis.
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